Lianne Smith, 45, who once worked in child protection services, used a plastic bag to kill her five-year-old daughter, Rebecca, and 11-month-old son, Daniel, at the Spanish seaside resort of Lloret de Mar before spending the night with their lifeless bodies.
On the opening day of her murder trial at the provincial court in Girona, north-east Spain, yesterday, the jury heard that Mrs Smith had been thrown into a panic following her partner's arrest at their home in Barcelona on May 7, 2010.
She became obsessed with the idea that British social services were in Spain to take their children away from her and so, just a few days later, she gathered baby bottles, food and clothes, and took them to the Costa Brava, where they checked into the Miramar Hotel.
Mrs Smith refused to answer questions from the prosecution when she appeared at the opening of her trial yesterday, but the jury was shown a harrowing video of a statement she made to police the day after her children died, filmed in a room next to where the killings took place.
It showed her sobbing as she told officers that she had given them a "perfect holiday" before she realised they had reached "the end of the road".
"I knew they were going to take my children to England," she told police. "My daughter didn't want to go. I know it's not right to take another life, but I felt I was in a corner and my intention was for me and my children to go. It was not just the children, it was me as well."
In the video tape, she went on to calmly describe how she held each of her children in her arms as she pressed a plastic bag over their faces.
"I ended the lives of my two children. Then I lay in the bed beside them. I gave them a cuddle," she told detectives.
Describing how she first killed Daniel, she said: "I put a bag on his head. All of the head was in. [I knew when he was dead] because I was holding him."
She said she then turned to her sleeping daughter Rebecca and killed her with the same bag.
That night she sat beside her dead children writing a series of notes. "I love you very much. I wanted to give you a lovely life together. I'm very sorry," read one.
Mrs Smith told police that she tried to cut her own wrists, her throat, and tried to drown herself, suffocate herself and hang herself with a telephone cable but had failed in her suicide attempts. It was only the next day, at 1.30pm, that she went to hotel reception and asked them to call the police and an ambulance.
Mrs Smith, a former child protection expert with Cumbria County Council, and her partner, Martin Smith, 46, had fled to Spain from Lichfield, Staffordshire, in 2007. The couple, who were unmarried despite sharing the same surname, fled after Mr Smith was accused of sexually abusing a young female.
They set up home in the Catalan capital, where she found work as an English teacher, and their son Daniel was born in 2009. They were finally tracked down to Barcelona and Mr Smith, who claimed to be a psychic and a hypnotist, was arrested. He was extradited back to Britain on the day of the killings.
He was jailed for 16 years in March 2011 for repeated sexual abuse. He was found hanged in his cell at Manchester's Strangeways prison in January.
Mrs Smith's defence lawyer said that she could not be held criminally responsible for the killings of her children because she was in a psychotic state.
Following the arrest of her partner, Mrs Smith had felt "persecuted, hounded and threatened," said Jenifer Lahoz Abos. She said Mrs Smith had a "total emotional dependence" on her partner and was left in "a state of psychosis" after his arrest.
"She thought [British social services] were going to come and take her children away and give them to other families in adoption, so she started to run," the lawyer said.
"She entered a state of panic and lost contact with reality, interpreting events in a totally distorted manner, with delirious beliefs that she was in danger and there was a serious threat to her life and that of her children."
Mrs Smith faces 38 years in prison if found guilty. The trial continues.